Electric discharge devices



Oct. 14, 1958 Filed March 18. 1954 G. H. HOUGH ET AL ELECTRIC DISCHARGE DEVICES 2 Sheets-Sheet l lnvenlors H.HOUGH Av H W B EC K- MJACKSON I. H. FRASER Aliorney Oct. 14, 1958 G. H. HOUGH ET AL 2,856,554

ELECTRIC DISCHARGE DEVICES Filed March 18. 1954 2 Sheets-Sheet 2 3/ 27 32 293?? a 3o (I 1 1 l ft gz I we; a a um! F5 F 5H g'iLgJiii 'Ull w m 3U EU EIIUJU Inventors G. H.HOUGH- A. H. W. BECK T. M. JACKSON I H.F RASER Attorney United States Patent 2,856,554 ELECTRIC DISCHARGE DEVICES George Hubert Hough, Arnold Hugh William Beck,

Thomas Meirion Jackson, and Ian Hugh Fraser, London, England, assignors to International Standard Electric Corporation, New York, N. Y.

The present invention relates to cold cathode gas-filled electric discharge tubes, and is concerned with means for eliminating the statistical delay of firing of discharge gaps within such tubes.

It is characteristic of cold cathode tubes that the necessary charged particles for allowing a gap to break down may be provided by such occurrences as cosmic rays or by the action of light ejecting photo-electrons from the cathode.

It is known to provide photon-producing means within gas tubes but the danger exists that the ionisation produced by the photon-producing means may have the effect of altering the striking potential of discharge gaps of the tube, and in other ways affecting the operation of the tube.

According to the present invention there is provided a cold-cathode gas-filled electric discharge tube comprising discharge gap electrodes including a cathode, means producing or adapted with the aid of circuit means external to the tube to produce photons ejecting photoelectrons from the said cathode, and means preventing charged particles from the said photon producing means from being transferred to any of the said discharge gap electrodes associated with the said cathode.

In some embodiments of the invention the means preventing access of charged particles to the discharge gaps may comprise simply the introduction of a quartz barrier between the photon producing means and the discharge gaps, while in others the photon producing means may be completely enclosed in a separate quartz envelope within the main envelope of the tube. In the embodiments to be described the photon producing means is an auxiliary glow discharge gap, although, particularly when the photon producing means is enclosed within its own envelope, the use of a radio-active substance is not excluded.

Embodiment of the invention will be described with reference to the accompanying drawings, in which:

Fig. 1 shows diagrammatically a cold cathode discharge tube having an auxiliary discharge gap contained within its own separate envelope Within the main tube envelope; and

Fig. 2 shows the application of the invention to a known type of cold cathode trigger tube.

In the embodiment of Fig. l, the tube is housed within a glass envelope 1 having a glass base 2 through which project leads 3. The electrode structure 4 comprises a main cathode 5, and a pair of anodes 6 and 7, together with auxiliary discharge gap electrodes 8 and 9 which are housed within a separate envelope 10, provided with its own exhaust and gas-filling tubulation 11. The e1cctrodes are shown supported between insulating washers 12 and 13 by means of eyelets 14 to which the electrode supports are welded, the insulating washers being spaced apart by means of rods 15. The electrode assembly 4' is supported on the leads 3 by means of the electrode connections 16. The envelope 10 surrounding the auxiliary electrodes may be filled with gas whose nature and Patented Oct. 14, 1958 pressure may be different, if desired, from that filling the main envelope 1. The nature of the material of the envelope 10 will be chosen in accordance with the photoelectric threshold of the discharge surface of cathode 5; in the case of an activated cathode having a low photoelectric threshold and therefore rendered photo-electron emitting by photons of low energy, this envelope could be of soda-lime glass. For use with a pure nickel cathode we have found that quartz is entirely satisfactory, nickel requiring light of a wave-length of some 2,500 Angstrom units to ensure photo-electron emission.

Fig. 2 shows the application of the present invention to a tube forming the subject-matter of our U. S. Patent No. 2,631,261 issued March 10, 1953. In this figure, the envelope 17 houses an electrode assembly 18 comprised of a main cathode 19 and a main anode 20 together with a trigger electrode 21 which is interposed between the end 22 of cathode 19 and the anode 20. The anode 20 is mounted on an insulator 23 and the cathode 19 and trigger electrode 21 are mounted on an insulator 24 backed by a further insulator 25 in order to shield the supports for the cathode 19 and trigger electrode 21. Auxiliary discharge gap electrodes, comprising an auxiliary anode 26 and an auxiliary cathode 27, are mounted upon an insulator 28. The auxiliary anode 26 has an aperture 29 opposite cathode 27. The spacing between the auxiliary anode 26 and auxiliary cathode 27 is such that the cathode glow of the auxiliary discharge is located within the aperture 29. The insulators 24 and 25 are apertured at 30 and 31, respectively, so that the glow discharge at the aperture 29 irradiates the tip 22 of the main cathode.

The tube is designed so that the main gap between cathode 19 and anode 20 is effectively shielded during normal operation from the auxiliary discharge, whose effect is merely to eliminate the statistical delay of firing of the trigger gap between the end 22 of cathode 19 and the trigger electrode 21, while not measurably lowering the breakdown potential of this trigger gap. Nevertheless, under certain conditions of use, outside the normal range of operation of the tube, it has been found possible to transfer some of the current flowing to the anode 20 from the main cathode 19 to the auxiliary cathode 27, the two cathodes thus sharing the discharge current. In this condition, when discharge at the main gap is extinguished by raising the potential of cathode 19, a discharge is maintained between the cathode 27 and anode 20 along the path indicated by the dotted line 32, through the trigger gap.

It has been found that the above-mentioned trouble can be completely cured, without in any way influencing the desired effect of the auxiliary discharge, by introducing a quartz barrier indicated at 33, between the two insulators 24 and 25 so as to cover the aperture 30. In this way charged particles are prevented from travelling to any of the discharge electrodes 19, 20 or 21, while photons from the auxiliary glow discharge are still allowed to fall on the end portion 22 of cathode 19, there liberating photo-electrons and so eliminating the statistical delay of firing of the trigger gap.

While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What we claim is:

A cold cathode electric discharge tube comprising an envelope, said envelope containing a gas filling, discharge gap electrodes including a main cathode and a main anode and a trigger electrode interposed between at least a portion of the said main cathode and the said main anode, auxiliary discharge gap electrodes, glow discharge between which irradiates the said main cathode to eliminate the statistical delay of firing of the gap between it and the said trigger electrode, a quartz barrier interposed between said auxiliary discharge gap electrodes and the other electrodes permeable to light of the wavelength required to eject photo-electrons from the said cathode, but impervious to charged particles tending to pass between the auxiliary and the other aforementioned electrodes.

References Cited in the file of this patent UNITED STATES PATENTS 

